IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: mayyoya92 on December 24, 2009, 03:41:57 pm

Title: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 24, 2009, 03:41:57 pm

HI ,i just wanted some 1  to solve this logarithmic equation for me , i'm very bad at logarithms!!
if ln(x)+3 ln(y)-ln(2) = ln(x power 4)-ln(54)   ,fimd the value of x/y??
 thanx                                                         

Title: Re: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 25, 2009, 06:38:42 pm

oh thank you all ,i'm having great help here!! >:( >:( >:(

Title: Re: A2 math cie HEEEEEELP!
Post by: 123 on December 26, 2009, 07:59:58 am

Well whats so hard bout it??

>> ln(x)+3 ln(y)-ln(2) = ln(x^4)-ln(54)

here follow log rules     
eg. ln(a) + ln(b) = ln(ab) 
     ln(a) - ln(b) = ln(a/b)       
     3ln(a) = ln(a^3)                 

>> ln(x) + ln(y^3) -  ln(2) = ln(x^4) -ln(54)
    ln(x.y^3) - ln(2) = ln(x^4) -ln(54)

just collect all x & y on 1side and whole nos. on other side
i.e,
 -ln(2) + ln(54) = ln(x^4) - ln(x.y^3)
ln(54) - ln(2) = ln ([x^4] / [x.y^3]) 
ln(54/2) = ln(x^3 / y^3)
ln(27) = ln(x/y)^3

try to solve it urself, heres a hint:
ln(a)=ln(2)
a = e^2   ----->anti-log

hope this is helpful  :D

Title: Re: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 26, 2009, 04:19:32 pm

thank you very much ;D

Title: Re: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 26, 2009, 09:54:59 pm

another question about trignometry and astec rules,if 3A=2A +A prove that sin3A -4sin(power3)A ,hence solve the equation 3sinA-4sin(power3)A = -root3 /2...i know how to prove it but i can't solve it!!

Title: Re: A2 math cie HEEEEEELP!
Post by: astarmathsandphysics on December 26, 2009, 10:53:05 pm

LHS=sin(3A) so 3A=arcsin(-sqrt(3)/2)=240, 300,600, 660
so solve 3A=240
2A=300
3A=600
3A=660

Title: Re: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 27, 2009, 02:24:41 pm

thank you very much but please could you explain the first part of your answer?

Title: Re: A2 math cie HEEEEEELP!
Post by: astarmathsandphysics on December 27, 2009, 02:41:57 pm

x=arcsina then do 180-x, 360+x, 540-x,720+x etc

Title: Re: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 28, 2009, 10:40:24 am

thank you very much! (i'm not so good at astc rules ::) ::)

Title: Re: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 28, 2009, 10:48:27 am

is there any website having eplanation of astc rules? thanx in advance.

Title: Re: A2 math cie HEEEEEELP!
Post by: astarmathsandphysics on December 28, 2009, 03:15:13 pm

http://www.astarmathsandphysics.com/a_level_maths_notes/C2/a_level_maths_notes_c2_finding_multiple_solutions_of_trigonometric_equations.html

Title: Re: A2 math cie HEEEEEELP!
Post by: mayyoya92 on December 29, 2009, 10:27:06 am

thanx a lot :D